brooklynwx99

To remove all ambiguity, I made another composite of the loading pattern for all NYC snowstorms of 15" or more from 1948 onward, four days before the event began. @PB GFI I think you were right about the 10 days, my bad. Here is the GEFS (which the EPS has been catching up to) for the 18th, about four days before the window for a possible EC storm (21-23rd): At this range, that is absolutely uncanny. The positive anomalies in the Arctic and near Hudson Bay are of the nearly the same strength and placement, and even the TPV lobe in SE Canada is seen. The trough off the WC is almost a mirror image. Again, history is now pointing to an extremely favorable synoptic setup, and I believe that the 21-23 period is the one to watch for an high-impact EC storm. The signal is astounding for this lead time.

I'm pretty sure when I made this it was the lag for 3-5 days before? Makes sense too, given that the blocking establishes itself a few days before the possible storm window. This is certainly a good period to watch, that strong blocking decaying over Hudson Bay is a classic signal.

This is such an amazing setup.

This scenario is why you're seeing the huge bomb solutions on ensembles for the 19-22nd time period. The TPV is displaced southward because of the interaction between the 16-18th shortwave, and it provides a deep, cold airmass while compressing heights and leading to persistent NW flow over the NE. A vigorous shortwave then comes ashore, originating from the active Pacific (-PNA). The trailing longwave trough is then able to pump heights ahead of it, creating a mid level ridge for the shortwave to roll off of, amplify, and possibly close off. That isn't even considering the 50/50 ULL providing an arctic anticyclone in SE Canada and the transient -NAO due to the wave break. It's honestly a pretty classic progression.

I feel that you have slightly misinterpreted my post. I don’t want TPV interaction for the 17-18th threat; I said that I wanted the interaction for the probable shortwave afterwards, as the TPV dropping down could put a nice antecedent airmass into place. I agree with you regarding this system though, we want a vigorous shortwave with little TPV interaction to keep it from getting tugged northward. This could certainly be the case given the ECMWF and its ensembles. I’m leaning towards more interaction than not, but it’s too early to make any definitive statements given the lead time.

I actually want more TPV interaction with the first system, as that strengthened interaction will: 1) Lead to a higher chance of a wave break, which would aid in developing NAO blocking, and 2) Lead to the delivery of a cold, dense air mass with abundant anticyclones in S Canada. The GFS has certainly heightened the interaction between the 17-18th SW and the TPV over the last model cycle or so: Due to the increased amplification of the longwave trough in the E US, the TPV has a higher chance of invading the N US and injecting very cold air into our region. The GEFS also has a strong -PNA, which is actually a good thing in this synoptic setup, as it leads to a wave train from the Pacific, and the maritime tropical air interacts with the continental arctic air left over from the TPV: There is also a pretty defined bend in the isopleths in the 50/50 region as well as a decaying -NAO block, which are all generally favorable synoptic features for a large-scale storm in the E US. Also, given the strong thermal gradient that could be present, a strong SLP would not even be needed to produce prolific precipitation; frontogenesis could be achieved solely through the two clashing airmasses. Overall, like @CooL, I have much more interest in the period after the 18th, as I expect this period to be much more favorable for a larger system. That period could also produce, but given the trends of a more amplified Pacific wave lead me to believe that this period has some more merit. Of course, this is very far out, but the pattern progression makes sense to me. We will have to see, but December looks exciting to say the least.

Hey guys! I know there's some real love for the BDB (Dec 26-27, 2010 Blizzard). I was assigned to do a small case study for my synoptic meteorology class, and I picked this storm since it's near and dear to me. I thought I would share it with you guys, for nostalgia, for learning purposes and even for some constructive criticism. Here you go! *P.S. this is why I haven't been commenting much on the anafront today, this commanded much more attention* Severe Eastern United States Winter Storm, 25-27 December 2010: Near record-breaking snowfall in the New York City Metro area By Kyle Leahy 1. Overview A historic storm impacted the New York City (NYC) metro region from 26-27 December 2010, with 20-30 inches of snow falling throughout the metro with 10-20 inches in Long Island (Fig. 24). 20.0” was reported in Central Park and 24.5” was reported in Brooklyn. The highest recorded total in NYC was 29.0” in Great Kills, Staten Island. The highest reported snowfall total in the metro was in Rahway, NJ; the storm total snowfall was 32”. The extreme snowfall totals were also accompanied by strong winds up to 50-70 mph gusts due to a strong pressure gradient as the surface low pressure (SLP) deepened to under 975mb. Areas from the Carolinas to Maine were impacted with 10-20 inches of snow as this system tracked along the coast throughout its lifecycle. The purpose of this study is to determine the mechanisms for such rapid deepening and crippling impacts to the NYC metro and immediate surrounding regions. This system is a classic Miller A nor’easter, and its development is representative of other historic eastern United States (US) winter storms. 2. Synoptic Setup The overall synoptic setup began with an amplifying upper-level ridge over the Western United States in response to a 500mb shortwave approaching British Columbia on 00 UTC 25 December. As a result, a deepening trough began to take form over the midsection of the country. The shortwaves in the northern and southern streams of the amplifying trough started to dig in the Plains region of the US (Fig. 1). As time passed on Christmas Day, the southern stream energy began to undercut the amplifying northern stream shortwave as the overall western US ridge continued to strengthen, with 564 dam heights penetrating into Canada (Figs. 2, 3). As a result of positive vorticity advection (PVA) into Louisiana and Mississippi, a weak SLP center began to form at 12 UTC. Along with the PVA, a developing 275mb jet streak also helped to aid upper level divergence (Fig. 13), as the SLP was located in the right entrance region. Strong frontogenetic forcing caused by the southern flow interacting with the cold entrenched airmass led to the elevated snow totals in Tennessee, Alabama, and Mississippi. (Fig. 14). The favorable overall setup for lift can also be visualized by Q-vector convergence over a large portion of the southern US (Fig. 15). Q-vector convergence is often indicative of uniform ascent over a region, as Q-vectors point towards regions of upward vertical motion. By 00 UTC 26 December, the two pieces of energy coalesced into a single longwave trough, and a more defined SLP began to materialize in northern Florida (Fig. 5). Selfdevelopment started to ramp up at this juncture, as advection solenoids began to take shape and the longwave trough began to tilt negatively. By 12 UTC, a 500mb upper level low (ULL) had formed as a result of cold air advection into the trough and the strengthening of the western US ridge; therefore, the SLP had deepened to under 1000mb and the 500mb trough became neutral. An extremely favorable upper level setup had developed, as dual jet streaks had formed along the eastern seaboard (Fig. 16). Like earlier in the storm’s development, these jet streaks aided in the rapid development of the system as it moved up the coast. The system had deepened to about 985mb by 00 UTC 27 December, and the ULL strengthened to under 528 dam as it moved towards the eastern coast of the US. At this point, defined conveyor belts had formed as the SLP approached peak strength (Fig. 22). Although the SLP was beginning to occlude, the general synoptic setup was still highly favorable for an axis of heavy snow over the NYC metro. A strong 300mb jet streak was remained along the coast with the SLP in the left exit region, leading to further divergence aloft (Fig. 18). Along with an anomalous jet streak, there was also intense differential 700-400mb PVA (Fig. 19). According to the quasi-geostrophic omega equation, differential PVA implies rising vertical motion. Due to both of these factors, there was ample synoptic scale lift, which, in part, led to the historic snowfall totals seen. Soon afterwards, the SLP began to occlude fully and become vertically stacked, as the 500mb ULL and SLP were located in the same area off of Cape Cod, MA. The SLP began to move towards colder air, as its center had entered a region of sub-5400m 1000-500mb thicknesses (Fig. 11). Soon after, another SLP center began to form at the triple point, indicating the eventual decay of the parent SLP (Fig. 12). 3. Mesoscale Setup The overall synoptic setup was very conducive for a major eastern US winter storm, but mesoscale features led to the historic totals found in and around the NYC metro; namely, a strong 850mb low level jet (LLJ) and associated frontogenesis. As the SLP had begun to rapidly intensify off of the eastern seaboard, there was intense easterly flow off of the Atlantic converging with the northerly surface flow over the northeast (NE) US. The powerful 850mb LLJ moving warm, moist air over the cold, dense air over the NE US led to the increase of the thermal gradient over time (Fig. 17). This increase of the thermal gradient over time is known as frontogenesis, and 850mb frontogenesis values were extremely high over the NYC metro into southern New England (Fig. 20). The frontogenesis remained even when the bulk of the forcing moved into Maine, which was crucial to achieving such high totals (Fig. 21). Overall, rising air associated with the intense frontogenesis partially led to the development of mesoscale snow banding over the NE. Along with the 850mb LLJ and the associated frontogenesis, there was also lift up to 700mb coinciding with a defined cold conveyor belt (CCB). Looking at the 700mb wind vectors, one could infer that there was also a 700mb LLJ, which provided further ascent up through the CCB. Minimum omega values bottomed out at under -15 Pa/s, which is indicative of strong upward motion (Fig. 22). Since the 850mb and 700mb ULLs were vertically stacked, the ascent was able to reach throughout the column, leading to intense precipitation rates. The RADAR presentation correlated greatly with the axis of highest frontogenesis and 700mb omega. There was an intense deformation band reaching from the Hudson Valley to southern New Jersey, which led to the extreme totals in the NYC metro (Fig. 23). 4. Conclusion In summation, an anomalously strong low pressure system impacted the southeast US, part of the Mid-Atlantic and NE US with the NYC metro in the crosshairs. Favorable synoptic conditions, including strong 200-300mb jet streaks, a strengthening western US upper level ridge, and intense differential PVA promoted the rapid development of a powerful SLP that tracked up the eastern seaboard. Along with the auspicious synoptic setup, the 850mb frontogenetic forcing and 700mb ascent due to vigorous LLJs helped generate persistent deformation banding over the NYC metro, which led to snowfall totals up to and above 24”. Figures: Figure 1. On left: 500mb heights and vorticity; on right: SLP and 1000-500m thicknesses, valid 00 UTC 25 December 2010. Figure 2. On left: 500mb heights and vorticity; on right: SLP and 1000-500m thicknesses, valid 06 UTC 25 December 2010. Figure 3. On left: 500mb heights and vorticity; on right: SLP and 1000-500m thicknesses, valid 12 UTC 25 December 2010. Figure 4. On left: 500mb heights and vorticity; on right: SLP and 1000-500m thicknesses, valid 18 UTC 25 December 2010. Figure 5. On left: 500mb heights and vorticity; on right: SLP and 1000-500m thicknesses, valid 00 UTC 26 December 2010. Figure 6. On left: 500mb heights and vorticity; on right: SLP and 1000-500m thicknesses, valid 06 UTC 26 December 2010. Figure 7. On left: 500mb heights and vorticity; on right: SLP and 1000-500m thicknesses, valid 12 UTC 26 December 2010. Figure 8. On left: 500mb heights and vorticity; on right: SLP and 1000-500m thicknesses, valid 18 UTC 26 December 2010. Figure 9. On left: 500mb heights and vorticity; on right: SLP and 1000-500m thicknesses, valid 00 UTC 27 December 2010. Figure 10. On left: 500mb heights and vorticity; on right: SLP and 1000-500m thicknesses, valid 06 UTC 27 December 2010. Figure 11. On left: 500mb heights and vorticity; on right: SLP and 1000-500m thicknesses, valid 12 UTC 27 December 2010. Figure 12. On left: 500mb heights and vorticity; on right: SLP and 1000-500m thicknesses, valid 18 UTC 27 December 2010. Figure 13. 275mb winds, isotachs, and geopotential height at 12 UTC 25 December 2010. Figure 14. GFS40 850-700mb frontogenesis at 12 UTC 25 December 2010. Figure 15. GFS40 400 mb Q-vectors (arrows) and Q-vector convergence (purple shades) and divergence (orange and red shades) six-hour forecast at 00 UTC 26 December 2010. Figure 16. 275mb winds, isotachs, and geopotential height at 12 UTC 26 December 2010. Figure 17. 850mb heights, temperature and wind speed at 00 UTC 27 December 2010. Figure 18. 300mb heights and wind speed at 00 UTC 27 December 2010. Figure 19. 500mb geopotential height (black contours), absolute vorticity (color fill) and 700-400 differential vorticity (blue contours) at 23 UTC 26 December 2010. Figure 20. 850mb frontogenesis (red contours) and 800-750mb saturated equivalent potential vorticity (shaded) at 23 UTC 26 December 2010. Figure 21. 850mb frontogenesis (red contours) and 800-750mb saturated equivalent potential vorticity (shaded) at 06 UTC 26 December 2010. Figure 22. 700mb heights, omega and relative humidity at 00 UTC 27 December 2010. Figure 23. RADAR imagery across the Eastern Seaboard at 23 UTC 26 December 2010. Figure 24. Observed snowfall totals from 24-28 December 2010. References: Ray’s Winter Storm Archive: http://www.raymondcmartinjr.com/weather/2011/26-Dec-10.html PSU NARR reanalysis: http://mp1.met.psu.edu/~fxg1/NARR/2010/us1225.php NESIS snowfall map: https://www.ncdc.noaa.gov/monitoring-content/snow-and-ice/rsi/nesis/20101224-20101228-4.92.jpg SPC mesoanalysis: https://www.spc.noaa.gov/exper/mesoanalysis/

It appears that the analog set that I presented in October will have a good chance of verifying due to the wave break in the Pacific. The subsequent -EPO/+PNA and +AO/NAO dipole is reminiscent of the 2013-15 seasons, and the two data sets are extremely similar: It's almost a dead ringer. The main pattern features are all there, so I feel like the upcoming pattern has more credence due to past analogs as well as the overall hemispheric support present. I also believe that the Dec 12-16 window will contain our next threat, as cold air will most likely be deeply entrenched into almost the entire northern half of the US and the TPV press will subside. The 12z GFS shows the idea well: As the TPV lobe moves into E Canada and Greenland, heights are able to decompress along with the injection of arctic air. Along with this development, a shortwave is able to detach itself from the Aleutian ULL and amplify due to the +PNA. Once the wave amplifies, heights are able to rebound into the EPO domain. Verbatim, this wave deepens and becomes an intense cyclone in the E US. Although this is a long range OP run, I believe that it displays the unique potential that this pattern could have if the wave break indeed comes to fruition. This is giving me flashbacks to 2013-2015, that's for sure. I'm very happy with how my analog set is performing thus far, and I believe that December will continue to provide opportunities for wintry weather throughout.

Looks like a Pacific Jet extension will lead to a wave break upstream, forcing a poleward mid-level ridge into the polar regions. This could definitely become a period of interest if energy comes over the ridge and amplifies in the trough:

Precip will blossom into the LHV and begin to pivot south into the NYC metro due to increased differential divergence and more favorable low-level moisture transport:

Here's the blossom and pivot: the NYC metro, the LHV, and NNJ/CNJ are going to be right in the crosshairs. Looks like some of our more promising dynamic events with strong convective echoes pushing onshore. The pivot also lines up well with the ageostrophic wind from the strong 300mb jet streak aloft:

I wouldn't put too much stock into the rather paltry precip outputs from the 12z 3km NAM or 14z HRRR given the low values of omega situated right in the DGZ:

The RGEM looks to have a better handle on radar as of now, as it picked up the heavier returns in NJ quite well. I would put more weight on its future radar depiction rather than the NAM, as it is also handling the SLP more effectively. Also, radar returns are lining up quite nicely with 925-850mb fgen, and the pivot is beginning to show up. I expect precipitation to blossom in the next hour with the area from the LHV south into Monmouth County in the crosshairs. If the banding signal is legit (which I think it is) the NYC metro can expect to see upwards of 6” with upwards of 12” in areas most highly affected. If NYC doesn’t get hit by the banding, I stick by my older forecast of 2-5”, but I expect the caveat I mentioned then to hold true given the more recent mesoscale developments.

Looks like the location of the SLP is quite similar to that of the 05z HRRR; in fact, the center might be slightly east of its progged location. I’m discounting the far eastern center, as it is most likely convective feedback, not a true SLP.

Looks like the HRDPS has a better handle on precipitation and SLP position than the 3km NAM. Seems like the 3km has a feedback issue with the convection to the east.